The present invention relates to a fuel injector-pressure sensor combination for fuel injection systems for direct injection of fuel into the combustion chamber of an internal combustion engine and for measurement of the pressure in the combustion chamber.
A fuel injector having a piezoelectric actuator is known, for example, from German Published Patent Application No 195 00 706. In this known fuel injector, the piezoelectric or magnetostrictive actuator activates a power piston which acts upon a reciprocating piston via a hydraulic path transformer. The reciprocating piston has a positive connection with a valve closer provided at the injection opening via a valve needle. The piezoelectric or magnetostrictive actuator therefore has a non-positive connection to the valve closer via the hydraulic path transformer. If an appropriate electrical voltage is applied to the actuator, it expands and displaces the power piston correspondingly. Even a relatively slight displacement of the power piston is transformed by the hydraulic path transformer into a considerably greater displacement of the reciprocating piston so that the valve closer clears the injection opening, leaving it with an adequate cross-section.
A fuel injector of similar design is derived from German Patent No 43 06 073. A housing-side support of the actuator in a special spherical disk bearing in particular is known from this printed publication in order to cause the piezoelectric actuator to have complete contact with the plunger it is to act on if the actuator end surfaces are slightly non-parallel.
For various applications, it is desirable to detect the pressure prevailing in the combustion chamber via a suitable sensor. For this purpose, it has heretofore been customary to provide pressure sensors in the cylinder head of the internal combustion engine as individual components and to measure the combustion pressure in the combustion chambers of the engine in this manner. Since present-day internal combustion engines have multiple intake and exhaust valves per combustion chamber and also in the case of direct injection, a spark plug to ignite the fuel is also necessary in the combustion chamber of an internal combustion engine having spark ignition in addition to a fuel injector for direct injection of the fuel into the combustion chamber, the available installation space on the cylinder head is very limited. Since a separate bore in the cylinder head is required for each pressure sensor designed as individual components, the practical implementation of pressure measurement in injection systems with direct injection into the combustion chamber is difficult.